1. Field of the Invention
The present invention relates to a retrofocus lens system suitable for a single-lens reflex camera and a digital camera, and an image-taking device.
2. Related Background Art
Focusing of an imaging lens is generally carried out by extending the whole lens system to an object side. However, when this focusing method is applied to a retrofocus type wide-angle lens, since variation in spherical aberration and astigmatism is large upon focusing on a close object, there happens to be a problem that good optical performance cannot be obtained. Accordingly, in order to preferably suppress variation in aberration upon focusing on a close object, there has been proposed a retrofocus lens system applying a floating method in such as Japanese Patent Application Laid-Open No. 2005-181852.
The lens system disclosed in Japanese Patent Application Laid-Open No. 2005-181852 is composed of, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. Upon focusing on a close object, the first lens group is fixed, a distance between the first lens group and the second lens group increases, and a distance between the second lens group and the third lens group decreases
However, since the second lens group has positive refractive power, distortion is generated excessively upon focusing to cause a problem. Moreover, since the first lens group is fixed upon focusing, sufficient correction of aberrations upon focusing on a close object cannot be carried out to cause another problem.